Perpendicular magnetic film, multilayered film for perpendicular magnetic film and process for producing perpendicular magnetic film

ABSTRACT

Disclosed herein is a perpendicular magnetic film comprising a spinel thin film which is formed on a substrate, which contains Fe as the main ingredient and further contains Co and Ni, and which has a coercive force of less than 3000 Oe, the plane (400) thereof being predominantly oriented in parallel with said substrate, the spacing of the plane (400) being not more than 2.082 Å, the molar ratio of Co to Fe being 0.005 to 0.32 and the molar ratio of Ni to Co being at least 0.6.

BACKGROUND OF THE INVENTION

The present invention relates to a perpendicular magnetic film. Moreparticularly, the present invention relates to a perpendicular magneticfilm which is composed of a spinel thin film containing Fe as the mainingredient and further containing Co and Ni, which has an excellentoxidation resistance, an excellent anticorrosivity, and an appropriatecoercive force for preventing a magnetic saturation of a magnetic headwhich is widely used at present, particularly, a coercive force of lessthan 3000 Oe, and hence, which is suitable as a high-density magneticrecording medium. The present invention also relates to a process forproducing such a perpendicular magnetic film, and a multilayered filmfor a perpendicular magnetic film which is used as an intermediate inthe production of the perpendicular magnetic film.

With recent remarkable tendency for miniaturized and higher reliableinformation processing apparatuses and systems, magnetic recording mediahave increasingly been required to have a higher recording density. Aperpendicular magnetic film as a magnetic recording medium which respondto such demand has been rapidly developed and put to practical use.Perpendicular magnetic films which are magnetized perpendicularly to thefilm surface are not only free from demagnetization but also capable ofhigh-density recording.

An alloy film such as a CoCr alloy film has conventionally been proposedas a perpendicular magnetic film. However, it is necessary to coat thesurface of a CoCr alloy film with a carbon film having a thickness ofabout 100 to 200 Å in order to prevent the deterioration of themagnetization characteristics. As a result, the spacing (the distancebetween a magnetic head and the recording medium) loss is increased bythe distance corresponding to the thickness of the carbon film, which isunsuitable for high-density recording. For this reason, a material of aperpendicular magnetic film is strongly required to be an oxide which isstable against oxidation.

As to the coercive force of a perpendicular magnetic film, anappropriate coercive for preventing a magnetic saturation of a magnetichead which is widely used at present, particularly, a coercive force ofless than 3000 Oe is required.

The coercive force (Hc) of a magnetic recording medium has a closerelationship with the performance of a magnetic head, as is well known.When the coercive force (Hc) of the magnetic recording medium is as highas more than 3000 Oe, the current at which a writing operation isperformed becomes so high that the head core of a magnetic head which iswidely used at present is magnetically saturated due to an insufficientsaturation flux density (Bm). As a result, it is impossible tosufficiently magnetize the magnetic recording medium.

A ferrite head is widely used in a magnetic recording and reading-outmachine which corresponds to a magnetic recording medium having acoercive force of not more than 1000 Oe, while a head such as a Sendusthead, an amorphous head and a thin-film head, whose head core is made ofa material having a high saturation flux density, is used in a magneticrecording and reading-out machine which corresponds to a magneticrecording medium having a coercive force of more than 1000 Oe.

As a perpendicular magnetic film for magnetic recording, an amorphousalloy film such as a CoCr alloy film and a CoPt alloy film, a spineloxide thin film such as a cobalt ferrite film (Japanese PatentApplication Laid-Open (KOKAI) Nos. 51-119999 (1976), 63-47359 (1988),3-17813 (1991), 3-188604 (1991) and 4-10509 (1992)), a magneto plumbiteoxide thin film such as a barium ferrite film (Japanese PatentApplication Laid-Open (KOKAI) No. 62-267949 (1987)) and the like haveconventionally been proposed.

Examples of the perpendicular magnetic recording films and processes forproducing the same which have conventionally been disclosed are setforth below, concretely.

(i) A process for producing a cobalt ferrite spinel film, whichcomprises forming a spinel film by sputtering onto a substrate of a lowtemperature in an oxidizing air by using an alloy target composed mainlyof Co and Fe (Japanese Patent Application Laid-Open (KOKAI) No.63-47359). In Japanese Patent Application Laid-Open (KOKAI) No.63-47359, the description of "When a reactive sputtering is carried outin an oxidizing air by using an alloy target composed mainly of Co andFe, a cobalt.ferrite spinel film represented by Co_(x) Fe_(3-x) O₄,(wherein 0.5≦x≦1.05) is formed on the substrate. In this case, even ifthe surface temperature is as low as about 200° C., a spinel film havinga good crystallizability is obtained." is disclosed.

(ii) A magnetic recording medium comprising a substrate, an under layerof a crystalline film having a spinel crystalline structure, and amagnetic recording layer of a spinel ferrite crystalline film, whereinthe lattice constant of the under layer is larger than that of themagnetic recording layer (Japanese Patent Application Laid-Open (KOKAI)No. 3-17813). The description of "The under layer is composed of amaterial represented by the following general formula:

    AB.sub.2 O.sub.4

wherein A is a metal element of divalent ions and at least one selectedfrom the group consisting of Mg, Mn, Co, Ni, Cu, Zn, Fe, etc., and B isa metal element of trivalent ions and at least one selected from thegroup consisting of Cr, In, Rh, Sc, Tl, Fe, etc. The magnetic recordinglayer 3 is composed of the material represented by the following generalformula:

    AB.sub.x Fe.sub.3-x O.sub.4

wherein A and B are the same as in the above-mentioned general formula,and 0≦x<2 ." is disclosed in Japanese Patent Application Laid-Open(KOKAI) No. 3-17813.

(iii) An oriented film of oxide crystals represented by the followinggeneral formula:

    A.sub.x B.sub.3-x O.sub.y

wherein A is at least one selected from the group consisting of Mn, Co,Ni, Cu, Mg, Cr, Zn, Li and Ti; B is Fe or Al;, 0.5≦x≦2.0 and 2.5≦y≦4,wherein the ratio (I₁₁₁ /I₂₂₂) of the reflective peak intensity I₁₁₁ ofthe crystal face (111) and the reflective peak intensity I₂₂₂ of thecrystal face (222) is less than 0.2 when the X-ray diffraction peak isindexed on the assumption that the film has a spinel crystallinestructure (Japanese Patent Application Laid-Open (KOKAI) No. 3-188604).

(iv) A process for producing a cobalt ferrite film comprising the stepsof forming a multi-layer metal film by laminating at least two of Colayer and Fe layer on a substrate, and heat-treating the obtainedmulti-layer film in an air containing oxygen (Japanese PatentApplication Laid-Open (KOKAI) No. 4-10509).

There are the following description in Japanese Patent ApplicationLaid-Open (KOKAI) No. 4-10509.

"The total thickness of the Co layer and the Fe layer in the multi-layermetal film is not more than 100 Å. This is because if the totalthickness of the Co layer and Fe layer exceeds 100 Å, it is difficult toproduce a cobalt ferrite film having a large Kerr rotation angle."

"Seven kinds of multilayers were formed on a glass substrate 3 (Coning7059, produced by CONING) by sputtering in Ar while using a single Cotarget and a single Fe target under the following condition, as shown inFIG. 1.

Sputtering condition:

Total sputtering pressure: 2 mtorr

Sputtering current: 0.2 A

Substrate temperature: room temperature

In each of the multilayers, the thickness ratio of a Co layer 1 and anFe layer 2 was 1:2, and the total film thickness was constantly 2000 Å.These multilayers obtained were 1 layer of (Co/Fe=660 Å/1340 Å) , 2layers of (Co/Fe=330 Å/670 Å), 4 layers of (Co/Fe=165 Å/335 Å) , 8layers of (Co/Fe=82.5 Å/167.5 Å), 10 layers of (Co/Fe=66 Å/134 Å), 20layers of (Co/Fe=33 Å/67 Å), and 40 layers of (Co/Fe=17 Å/33 Å). Each ofthe multilayers was heat-treated in an electric oven in the air in theheat treatment pattern shown in FIG. 3. More specifically, the film washeated at a high raising rate until 300° C., and then heated at araising rate of 100° C./hr until 500° C. The film was heated at 500° C.for 2 hours, and was then gradually cooled. Thus, a cobalt ferrite filmwas formed on the glass substrate."

Namely, the cobalt ferrite films disclosed in Japanese PatentApplication Laid-Open (KOKAI) No. 4-10509 are a multilayer (in-planemagnetic film) composed of a cobalt layer and a ferrite layer and a film(perpendicular magnetic film) composed of a cobalt.ferrite oxide. Eachof the multi-layer metal films is heat-treated at a temperature of notlower than 500° C. for not less than 2 hours, thereby obtaining acobalt.ferrite oxide film.

(v) An amorphous alloy film such as a Gd--Co film and a Tb--Fe film,composed of a rare earth metal and a transition metal (Japanese PatentApplication Laid-Open (KOKAI) No. 51-119999) and a magneto-plumbiteoxide thin film such as a barium ferrite film (Japanese PatentApplication Laid-Open (KOKAI) No. 62-267949).

Among the above-described perpendicular magnetic films, the cobaltferrite films which are typical of spinel oxides are stable againstoxidation, because they are oxides, and have a large crystallinemagnetic anisotropy. Owing to these magnetic characteristics the cobaltferrite films are considered to be promising as a perpendicular magneticrecording medium.

As the process for producing a cobalt ferrite (CoFe₂ O₄) film, variousmethods such as sputtering method, vacuum evaporation method and MO-CVDmethod are known.

However, although a perpendicular magnetic film which has an excellentoxidation resistance, an excellent anticorrosivity, and an appropriatecoercive force for preventing a magnetic saturation of a head which iswidely used at present is now in the strongest demand, none of theconventional magnetic thin films sufficiently meet these requirements.

For example, a cobalt ferrite (CoFe₂ O₄) film produced by a sputteringmethod is disadvantageous in that although the easy magnetization axisof a cobalt ferrite (CoFe₂ O₄) film is (100) axis to the plane (400),the plane (400) is likely to orient at random or the plane (111) islikely to orient in parallel with the substrate, so that it is difficultto produce a perpendicular magnetic film. As examples of a method forobtaining a cobalt ferrite (CoFe₂ O₄) film in which the plane (400) ispredominantly oriented in parallel with the substrate, (1) the methoddescribed in Proceedings of the 9-th Meeting of Magnetic Society ofJapan 29PB-10, (2) the method described in Proceedings of the 13-thMeeting of Magnetic Society of Japan, p 246, and (3) the methoddescribed in Japanese Patent Application Laid-Open (KOKAI) No. 4-10509(1992) are known.

The method (1) is a method of depositing Fe and Co ionized in an oxygenplasma on an MgAl₂ O₄ substrate or a silica glass substrate heated to500° C. Since it is necessary to maintain the substrate temperature at ahigh temperature such as not lower than 500° C. during film formation,the productivity is poor. In addition, in order to raise the substratetemperature to not lower than 500° C., the substrate itself is requiredto have a high heat-resistance. However, the heat-resistance of glassplastics or the like, which is widely used as a material of thesubstrate for a perpendicular magnetic recording medium, isinsufficient. In this way, since the material of the substrate islimited, it is not advantageous either industrially or economically.

The method (2) is a plasma-excitation MO-CVD method. Since it isnecessary to maintain the substrate temperature at 300° to 400° C. in avacuum during film formation, the productivity is poor, which isindustrially and economically disadvantageous.

The method (3) is a method of annealing a multilayered metal filmproduced by laminating at least two layers of Co and Fe at a temperatureof not lower than 500° C. in an atmosphere containing oxygen. Since ahigh temperature is necessary, the material of the substrate is limited,as described above, which is disadvantageous industrially andeconomically.

Accordingly, it is required to eliminate the above-described problems inthe related art and to provide a perpendicular magnetic film which iscomposed of an oxide having a spinel crystal structure, and which has anexcellent oxidation resistance, an excellent anticorrosivity and anappropriate coercive force.

Also, it is a technical problem to be solved of the present invention toprovide a process for producing a perpendicular magnetic film of anoxide having a spinel crystal structure and showing an excellentoxidation resistance, an excellent anticorrosivity and an appropriatecoercive force, at a temperature of lower than 500° C. and as low aspossible with industrial and economical advantages.

As a result of the present inventors' studies, it has been found that byannealing a Co- and Ni-containing multilayered film comprising as oneunit a magnetite [FeOx·Fe₂ O₃ (0<x≦1)] layer which contains or does notcontain Co and/or Ni and an oxide layer which contains Co and/or Ni(provided that the magnetite layer and the oxide layer are multilayeredso as to contain both Co and Ni as a whole unit), which are formed asubstrate, the plane (400) of the multilayered film being predominantlyoriented in parallel with the substrate, the thickness of one unit beingnot more than 300 Å, the molar ratio of Co to Fe being 0.005 to 0.32,and the molar ratio of Ni to Co being not less than 0.6, at atemperature of 280° to 450° C., the thus-obtained perpendicular magneticfilm an excellent oxidation resistance, an excellent anticorrosivity andan appropriate coercive force, for example, less than 3,000 Oe. On thebasis of the finding, the present invention has been attained.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a perpendicularmagnetic film which is composed of an oxide having a spinel crystalstructure, and which has an excellent oxidation resistance, an excellentanticorrosivity and an appropriate coercive force.

To achieve this aim, in a first aspect of the present invention, thereis provided a perpendicular magnetic film comprising a spinel thin filmformed on a substrate, which contains Fe as the main ingredient andfurther contains Co and Ni, in which the plane (400) is predominantlyoriented in parallel with the substrate, the spacing of the plane (400)is not more than 2.082 Å, the molar ratio of Co to Fe is 0.005 to 0.32and the molar ratio of Ni to Co is at least 0.6, and which has acoercive force of less than 3000 Oe.

In a second aspect of the present invention, there is provided a Co- andNi-containing multilayered film comprising a multiplicity of unitsformed on a substrate, each unit composed of a magnetite [FeOx·Fe₂ O₃(0<x≦1)] layer which contains or does not contain Co and/or Ni and anoxide layer which contains Co and/or Ni (provided that the magnetitelayer and the oxide layer are multilayered so as to contain both Co andNi as a whole unit), the plane (400) thereof being predominantlyoriented in parallel with the substrate, one unit having a thickness ofnot more than 300 Å, the molar ratio of Co to Fe is 0.005 to 0.32, andthe molar ratio of Ni to Co being at least 0.6.

In a third aspect of the present invention, there is provided a processfor producing the perpendicular magnetic film as defined in the firstaspect, comprising annealing the Co- and Ni-containing multilayered filmas defined in the second aspect at a temperature of 280° to 450° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) to 1(c) show the X-ray diffraction spectra of multilayeredfilms;

FIG. 2 shows the magnetization curves of the perpendicular magnetic filmobtained in Example 1;

FIG. 3 shows the magnetization curves of the perpendicular magnetic filmobtained in Example 2;

FIG. 4 shows the magnetization curves of the perpendicular magnetic filmobtained in Example 3;

FIG. 5 shows the magnetization curves of the perpendicular magnetic filmobtained in Example 4;

FIG. 6 shows the magnetization curves of the perpendicular magnetic filmobtained in Example 5;

FIG. 7 shows the magnetization curves of the perpendicular magnetic filmobtained in Example 6; and

FIG. 8 shows the magnetization curves of the film obtained inComparative Example 4.

DETAILED DESCRIPTION OF THE INVENTION

A perpendicular magnetic film according to the present invention is aspinel thin film formed on a substrate, containing Fe as the mainingredient and further containing Co and Ni. The plane (400) of theperpendicular magnetic film formed on a substrate is predominantlyoriented in parallel with the substrate and the spacing of the plane(400) of the perpendicular magnetic film is not more than 2.082 Å,preferably 2.070 to 2.080 Å. The molar ratio of Co to Fe in the thinfilm is 0.005 to 0.32, preferably 0.01 to 0.20 and the molar ratio of Nito Co therein is not less than 0.6, preferably 1.0 to 5.0. The coerciveforce of the perpendicular magnetic film is less than 3000 Oe,preferably 1200 to 2500 Oe.

In the present invention, the spacing of the plane (400) in the spinelthin film containing Fe as the main ingredient and further containing Coand Ni is not more than 2.082 Å. The spinel thin film of the presentinvention is a thin film wherein Fe²⁺ in the magnetite which constitutesthe multilayered film is completely oxidized into Fe³⁺, and alsoincludes a thin film in which a slight amount of Fe²⁺ in the magnetiteremains.

When the plane (400) of a film is not predominantly oriented in parallelwith the substrate, or when the spacing of the plane (400) of a filmexceeds 2.082 Å, the magnetization film does not constitute aperpendicular magnetic film.

If the molar ratio of Co to Fe is less than 0.005, it is difficult toproduce a perpendicular magnetic film. In order to facilitate theproduction of a spinel thin film in which the plane (400) ispredominantly oriented in parallel with the substrate, the molar ratioof Co to Fe is preferably not less than 0.01. If the molar ratio of Coto Fe exceeds 0.32, it is difficult to oxidize a magnetite, in otherwords, to transform magnetite [FeOx·Fe₂ O₃ (0<x≦1)] into γ-Fe₂ O₃, or todiffuse the Co ions and Ni ions in the spinel oxide layer composed of Feas the main ingredient at a temperature of not higher than 450° C.

If the molar ratio of Ni to Co is less than 0.6, it is difficult toobtain a perpendicular magnetic film having a coercive force of lessthan 3000 Oe. In order to obtain a coercive force of not more than 2500Oe, which is more preferable from the point of view of prevention of themagnetic saturation of a magnetic head, the molar ratio of Ni to Co ispreferably not less than 1.0. The larger the Ni content, the smaller thecoercive force is apt to become. With consideration for a preferablecoercive force, the upper limit of the molar ratio of Ni to Co is notmore than 5.0, preferably not more than 3.0. When the molar ratio of Nito Co is 5.0, the coercive force is about 800 Oe, and when the molarratio of Ni to Co is 3.0, the coercive force is about 1300 Oe.

If the coercive force of a perpendicular magnetic film of the presentinvention is more than 3000 Oe, it is impossible to prevent a magneticsaturation of a magnetic head which is widely used at present. From thepoint of view of prevention of the magnetic saturation of a magnetichead, the coercive force is preferably not more than 2500 Oe, morepreferably 1200 to 2500 Oe.

A perpendicular magnetic film according to the present invention isproduced by annealing at a temperature of 280° to 450° C., preferably290° to 400° C. a Co- and Ni-containing multilayered film composed of asone unit a magnetite [FeOx·Fe₂ O₃ (0<x≦1)] layer which contains or doesnot contain Co and/or Ni and an oxide layer which contains Co and/or Ni(provided that the magnetite layer and the oxide layer are multilayeredso as to contain both Co and Ni as a whole unit), which are formed on asubstrate, wherein the plane (400) is predominantly oriented in parallelwith the substrate, one unit has a thickness of not more than 300 Å, themolar ratio of Co to Fe is 0.005 to 0.32, and the molar ratio of Ni toCo is at least 0.6.

A multilayered film according to the present invention is a Co- andNi-containing multilayered film composed of a multiplicity of unitsformed on a substrate, each unit composed of a magnetite [FeOx·Fe₂ O₃(0<x≦1)] layer which contains or does not contain Co and/or Ni and anoxide layer which contains Co and/or Ni (provided that the magnetitelayer and the oxide layer are multilayered so as to contain both Co andNi as a whole unit). Such a multilayered film can be produced by any ofa reactive sputtering method in which a composite metal target (composedof an Fe target which contains or does not contain Co and/or Ni, and ametal target which contains one selected from Co, Ni, Co--Ni alloy, andCo and Ni) are sputtered in an oxidizing atmosphere; a direct method inwhich an oxidized film is directly formed from a sintered target ofmagnetite [FeOx·Fe₂ O₃ (0<x≦1)] which contains or does not contain Coand/or Ni and a sintered target of an oxide which contains Co and/or Ni;and a reactive evaporation method in which metals (Fe which contains ordoes not contain Co and/or Ni, and one selected from the groupconsisting of Co, Ni, Co--Ni alloy, and Co and Ni) are evaporated in anoxidizing atmosphere.

An example of layers which constitutes the unit in the Co- andNi-containing multilayered film used in the present invention is asfollows.

(1) Co- and Ni-containing magnetite layer/Co oxide layer

(2) Co- and Ni-containing magnetite layer/Ni oxide layer

(3) Co- and Ni-containing magnetite layer/Co and Ni oxides layer

(4) Co-containing magnetite layer/Ni oxide layer

(5) Co-containing magnetite layer/Co and Ni oxides layer

(6) Ni-containing magnetite layer/Co oxide layer

(7) Ni-containing magnetite layer/Co and Ni oxides layer

(8) Magnetite layer/Co and Ni oxides layer

The Co oxide layer is composed of Co oxide having NaCl-type crystallinestructure and the Ni oxide layer is composed of Ni oxide havingNaCl-type crystalline structure. Also, the Co and Ni oxides layer iscomposed of Co and Ni oxides having NaCl-type crystalline structure.

As the material of the substrate in the present invention, commerciallyavailable materials such as soda-lime glass are usable.

In a multilayered film according to the present invention, the thicknessof one unit is not more than 300 Å, preferably 50 to 250 Å, and themolar ratio of Co to Fe is 0.005 to 0.32. It is difficult to obtain aperpendicular magnetic film according to the present invention by usinga multilayered film in which the thickness of one unit exceeds 300 Å ora multilayered film in which the molar ratio of Co to Fe is less than0.005 or more than 0.32.

The molar ratio of Ni to Co in the multilayered film of the presentinvention is at least 0.6. If it is less than 0.6, the coercive force ofthe perpendicular magnetic film obtained by annealing the multilayeredfilm exceeds 3000 Oe.

The multilayered film of the present invention is composed of at leastthree units, each unit being composed of a magnetite [FeOx·Fe₂ O₃(0<x≦1)] layer which contains or does not contain Co and/or Ni and anoxide layer which contains Co and/or Ni (provided that the magnetitelayer and the oxide layer are multilayered so as to contain both Co andNi as a whole unit). Since the thickness of a perpendicular magneticfilm is preferably about 500 to 5000 Å, more preferably 500 to 3000 Å inpractical use, the number of units is determined so as to produce a filmof a desired thickness.

The annealing temperature of the multilayered film of the presentinvention is 280° to 450° C., preferably 290° to 400° C. The annealingtime is preferably 0.8 to 5 hours. If the annealing temperature is lowerthan 280° C., the oxidation of the magnetite [FeOx·Fe₂ O₃ (0<x≦1)],i.e., the transformation of magnetite [FeOx·Fe₂ O₃ (0<x≦1)] into γ-Fe₂O₃ or the diffusion of Co and Ni in the spinel thin film composed of Feas the main ingredient is insufficient for obtaining a perpendicularmagnetic film of the present invention. If the annealing temperatureexceeds 450° C., the transformation γ-Fe₂ O₃ into α-Fe₂ O₃ begins totake place so that it is impossible to produce a perpendicular magneticfilm according to the present invention.

In annealing, the transformation temperature for oxidizing the magnetite[FeOx·Fe₂ O₃ (0<x≦1)] i.e. transforming magnetite [FeOx·Fe₂ O₃ (0<x≦1)]into γ-Fe₂ O₃ is lowered by adding Cu to the spinel thin film, asdescribed in, for example, Japanese Patent Application Laid-Open (KOKAI)No. 57-54309 (1982). It is possible to produce a similar effect byadopting this method in the present invention. Annealing may be carriedout in two stages: the magnetite [FeOx·Fe₂ O₃ (0<x≦1)] is first oxidized(FeOx·Fe₂ O₃ (0<x≦1) is first transformed into γ-Fe₂ O₃) at atemperature of 240° to 320° C., and Co and Ni are then diffused at atemperature of 280° to 450° C. In this case, it is possible to suppressthe production of a crack which is likely to be caused during theoxidation of the magnetite (transformation of FeOx·Fe₂ O₃ (0<x≦1) intoγ-Fe₂ O₃).

What is the most important in the present invention is that theperpendicular magnetic film of the present invention is produced byannealing a Co- and Ni-containing multilayered film composed of amultiplicity of units formed on a substrate, each unit composed of amagnetite [FeOx·Fe₂ O₃ (0<x≦1)] which contains or does not contain Coand/or Ni and an oxide layer which contains Co and/or Ni (provided thatthe magnetite layer and the oxide layer are multilayered so as tocontain both Co and Ni as a whole unit), wherein the plane (400) thereofis predominantly oriented in parallel with the substrate, one unit has athickness of not more than 300 Å, the molar ratio of Co to Fe is 0.005to 0.32, and the molar ratio of Ni to Co is not less than 0.6.

This has been confirmed from the fact that a perpendicular magnetic filmaccording to the present invention cannot be obtained either by using amultilayered film in which the molar ratio of Co to Fe is between 0.005and 0.32 but, the thickness of one unit composed of a magnetite[FeOx·Fe₂ O₃ (0<x≦1)] layer which contains or does not contain Co and/orNi and an oxide layer which contains Co and/or Ni (provided that themagnetite layer and the oxide layer are multilayered so as to containboth Co and Ni as a whole unit) exceeds 300 Å, so that the planes (311)and (222) are predominantly oriented in parallel with the substrate, orby using a multilayered film in which the thickness of one unit of amagnetite [FeOx·Fe₂ O₃ (0<x≦1)] layer which contains or does not containCo and/or Ni and an oxide layer which contains Co and/or Ni (providedthat the magnetite layer and the oxide layer are multilayered so as tocontain both Co and Ni as a whole unit) is not more than 300 Å, but themolar ratio of Co to Fe is not in the range of 0.005 to 0.32, so thatthe plane (400) thereof is predominantly oriented in parallel with thesubstrate as shown in later-described Comparative Examples 3 and 4, andin FIGS. 1(a) and 1(b).

The coercive force of a conventional cobalt ferrite (CoFe₂ O₄) film isdependent upon the Co content, and the more the Co content thereinincreases, the more the coercive force thereof raises. On the otherhand, the coercive force of a perpendicular magnetic film of the presentinvention is not largely dependent upon the Co content but isapproximately determined by the molar ratio of Ni to Co. For thisreason, it is possible to control the coercive force of theperpendicular magnetic film only by the molar ratio of Ni to Co and toobtain a desired coercive force with stability and good reproducibility.

The reason why the perpendicular magnetic film of the present inventionis not largely dependent upon the Co content is considered to be asfollows.

The coercive force of a conventional cobalt ferrite (CoFe₂ O₄) film ischanged by utilizing the crystalline magnetic anisotropy. In contrast,in a perpendicular magnetic film of the present invention, the spacingof the plane (400) thereof is not more than 2.082 Å, as shown in thelater-described example, which is even smaller than 2.086 Å which is thespacing of the plane (400) of γ-Fe₂ O₃ which have the smallest spacingof the plane (400) in any other spinel crystal structure mainly composedof Fe. From these facts, it has been considered that themagnetostrictive anisotropy due to the strain of the lattice is impartedto the perpendicular magnetic film of the present invention in additionto the crystalline magnetic anisotropy due to cobalt.

That the small spacing of the perpendicular magnetic film of the presentinvention is not caused by the shrinkage or the like of the substratebut is due to the film itself has been confirmed from the fact that thespacing of the film produced by transforming a monolayer Fe₃ O₄ film(2000 Å) in which the plane (222) thereof is oriented in parallel withthe same glass substrate as that of the perpendicular magnetic film ofthe present invention into a γ-Fe₂ O₃ film was 2.407 Å, which isapproximately the same as 2.408 Å of the bulk value.

A perpendicular magnetic film of the present invention has a coerciveforce of not more than 3000 Oe, preferably 1200 to 2500 Oe, a saturationmagnetization of not less than 200 emu/cc (2500 G) , and a squareness ofnot less than 0.20, preferably not less than 0.40.

The perpendicular magnetic film of the present invention is excellent inoxidation resistance and anticorrosivity, because the perpendicularmagnetic film is composed of an oxide, and is suitable as a magneticrecording medium for high-density magnetic recording, because theperpendicular magnetic film comprises a spinel thin film composed of Feas the main ingredient which has an appropriate coercive force,particularly, a coercive force of less than 3000 Oe.

According to a process for producing a perpendicular magnetic film ofthe present invention, it is not necessary to heat the substrate to notlower than 300° C. during film formation in a vacuum, and it is possibleto produce a perpendicular magnetic film by annealing at a lowtemperature such as not higher than 500° C. The process of the presentinvention is therefore very advantageous both industrially andeconomically.

EXAMPLES

The present invention will be explained in more detail hereinunder withreference to the following examples and comparative examples.

In the following examples and comparative examples, the magneticcharacteristics were measured by using "Vibration Sample MagnetometerVSM-3S-15", manufactured by Toei Kogyo K.K.

Example 1

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 200° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 60 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar ratio of Ni to Co is 1.1) to a thickness of 5 Å as a secondlayer by sputtering the Co--Ni target at a deposition rate of 42 Å/min.The first layer and the second layer constituted one unit having athickness of 65 Å. The molar ratio of Co to Fe in one unit was 0.06.These operations were alternately repeated 68 times to obtain amultilayered film composed of 34 Fe₃ O₄ layers each having a thicknessof 60 Å, and 34 Co- and Ni-containing oxide layers each having athickness of 5 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate, as shown in the X-ray diffraction spectrum in FIG. 1(c).

The obtained multilayered film was annealed in the air at a temperatureof 350° C. for 2 hours so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

The magnetization curve of the thus-obtained spinel thin film is shownin FIG. 2. In FIG. 2, the solid line a shows the magnetization curve ofthe spinel thin film to which a magnetic field was applied in theperpendicular direction, and the broken line b shows the magnetizationcurve of the spinel thin film to which a magnetic field was applied inthe in-plane direction. As shown in FIG. 2, since the residualmagnetization and the coercive force of the solid line a were largerthan those of the broken line b, the spinel thin film was recognized asa perpendicular magnetic film. As to the magnetic characteristics of theperpendicular magnetic film, the saturation magnetization was 260 emu/cc(3300 G), the coercive force was 2.2 kOe, and the squareness was 0.63.The spacing of the plane (400) was 2.077 Å.

Example 2

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 280° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 54 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar ratio of Ni to Co is 1.1) to a thickness of 6 Å as a secondlayer by sputtering the Co--Ni target at a deposition rate of 42 Å/min.The first layer and the second layer constituted one unit having athickness of 60 Å. The molar ratio of Co to Fe in one unit was 0.08.These operations were alternately repeated 68 times to obtain amultilayered film composed of 34 Fe₃ O₄ layers each having a thicknessof 54 Å, and 34 Co- and Ni-containing oxide layers each having athickness of 6 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate.

The obtained multilayered film was annealed in the air at a temperatureof 400° C. for 1 hour so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

The magnetization curve of the thus-obtained spinel thin film is shownin FIG. 3. In FIG. 3, the solid line a shows the magnetization curve ofthe spinel thin film to which a magnetic field was applied in theperpendicular direction, and the broken line b shows the magnetizationcurve of the spinel thin film to which a magnetic field was applied inthe in-plane direction. As shown in FIG. 3, since the residualmagnetization and the coercive force of the solid line a were largerthan those of the broken line b, the spinel thin film was recognized asa perpendicular magnetic film. As to the magnetic characteristics of theperpendicular magnetic film, the saturation magnetization was 240 emu/cc(3000 G), the coercive force was 2.2 kOe, and the squareness was 0.64.The spacing of the plane (400) was 2.076 Å.

Example 3

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 180° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 54 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar ratio of Ni to Co is 1.1) to a thickness of 9 Å as a secondlayer by sputtering the Co--Ni target at a deposition rate of 42 Å/min.The first layer and the second layer constituted one unit having athickness of 63 Å. The molar ratio of Co to Fe in one unit was 0.12.These operations were alternately repeated 68 times to obtain amultilayered film composed of 34 Fe₃ O₄ layers each having a thicknessof 54 Å, and 34 Co- and Ni-containing oxide layers each having athickness of 9 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate.

The obtained multilayered film was annealed in the air at a temperatureof 400° C. for 1 hour so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

The magnetization curve of the thus-obtained spinel thin film is shownin FIG. 4. In FIG. 4, the solid line a shows the magnetization curve ofthe spinel thin film to which a magnetic field was applied in theperpendicular direction, and the broken line b shows the magnetizationcurve of the spinel thin film to which a magnetic field was applied inthe in-plane direction. As shown in FIG. 4, since the residualmagnetization and the coercive force of the solid line a were largerthan those of the broken line b, the spinel thin film was recognized asa perpendicular magnetic film. As to the magnetic characteristics of theperpendicular magnetic film, the saturation magnetization was 210 emu/cc(2700 G), the coercive force was 2.1 kOe, and the squareness was 0.57.The spacing of the plane (400) was 2.077 Å.

Example 4

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 280° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 80 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar ratio of Ni to Co is 1.5) to a thickness of 9 Å as a secondlayer by sputtering the Co--Ni target at a deposition rate of 4 2 Å/min.The first layer and the second layer constituted one unit having athickness of 89 Å. The molar ratio of Co to Fe in one unit was 0.07.These operations were alternately repeated 68 times to obtain amultilayered film composed of 34 Fe₃ O₄ layers each having a thicknessof 80 Å, and 34 Co- and Ni-containing oxide layers each having athickness of 9 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate.

The obtained multilayered film was annealed in the air at a temperatureof 400° C. for 1 hour so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

The magnetization curve of the thus-obtained spinel thin film is shownin FIG. 5. In FIG. 5, the solid line a shows the magnetization curve ofthe spinel thin film to which a magnetic field was applied in theperpendicular direction, and the broken line b shows the magnetizationcurve of the spinel thin film to which a magnetic field was applied inthe in-plane direction. As shown in FIG. 5, since the residualmagnetization and the coercive force of the solid line a were largerthan those of the broken line b, the spinel thin film was recognized asa perpendicular magnetic film. As to the magnetic characteristics of theperpendicular magnetic film, the saturation magnetization was 230 emu/cc(2900 G), the coercive force was 2.0 kOe, and the squareness was 0.61.The spacing of the plane (400) was 2.074 Å.

Example 5

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 200° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 56 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar ratio of Ni to Co is 2.7) to a thickness of 7 Å as a secondlayer by sputtering the Co--Ni target at a deposition rate of 42 Å/min.The first layer and the second layer constituted one unit having athickness of 63 Å. The molar ratio of Co to Fe in one unit was 0.05.These operations were alternately repeated 68 times to obtain amultilayered film composed of 34 Fe₃ O₄ layers each having a thicknessof 56 Å, and 34 Co- and Ni-containing oxide layers each having athickness of 7 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate.

The obtained multilayered film was annealed in the air at a temperatureof 400° C. for 1 hour so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

The magnetization curve of the thus-obtained spinel thin film is shownin FIG. 6. In FIG. 6, the solid line a shows the magnetization curve ofthe spinel thin film to which a magnetic field was applied in theperpendicular direction, and the broken line b shows the magnetizationcurve of the spinel thin film to which a magnetic field was applied inthe in-plane direction. As shown in FIG. 6, since the residualmagnetization and the coercive force of the solid line a were largerthan those of the broken line b, the spinel thin film was recognized asa perpendicular magnetic film. As to the magnetic characteristics of theperpendicular magnetic film, the saturation magnetization was 210 emu/cc(2700 G), the coercive force was 1.3 kOe, and the squareness was 0.48.The spacing of the plane (400) was 2.075 Å.

Example 6

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 200° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 130 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar ratio of Ni to Co is 1.5) to a thickness of 6 Å as a secondlayer by sputtering the Co--Ni target at a deposition rate of 30 Å/min.The first layer and the second layer constituted one unit having athickness of 136 Å. The molar ratio of Co to Fe in one unit was 0.015.These operations were alternately repeated 30 times to obtain amultilayered film composed of 15 Fe₃ O₄ layers each having a thicknessof 130 Å, and 15 Co- and Ni-containing oxide layers each having athickness of 6 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate.

The obtained multilayered film was annealed in the air at a temperatureof 380° C. for 2 hours so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

The obtained magnetization curve of the thus-obtained spinel thin filmis shown in FIG. 7. In FIG. 7, the solid line a shows the magnetizationcurve of the spinel thin film to which a magnetic field was applied inthe perpendicular direction, and the broken line b shows themagnetization curve of the spinel thin film to which a magnetic fieldwas applied in the in-plane direction. As shown in FIG. 7, since theresidual magnetization and the coercive force of the solid line a werelarger than those of the broken line b, the spinel thin film wasrecognized as a perpendicular magnetic film. As to the magneticcharacteristics of the perpendicular magnetic film, the saturationmagnetization was 280 emu/cc (3500 G), the coercive force was 2.0 kOe,and the squareness was 0.64. The spacing of the plane (400) was 2.070 Å.

Example 7

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 200° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 200 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar of Ni to Co is 1.5) to a thickness of 15 Å as a second layerby sputtering the Co--Ni target at a deposition rate of 30 Å/min. Thefirst layer and the second layer constituted one unit having a thicknessof 215 Å. The molar ratio of Co to Fe in one unit was 0.035. Theseoperations were alternately repeated 18 times to obtain a multilayeredfilm composed of 9 Fe₃ O₄ layers each having a thickness of 200 Å, and 9Co- and Ni-containing oxide layers each having a thickness of 15 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate.

The obtained multilayered film was annealed in the air at a temperatureof 380° C. for 3 hours so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

Since the residual magnetization and the coercive force of thethus-obtained spinel thin film represented by the magnetization curvesof the spinel thin film to which a magnetic field was applied in theperpendicular direction were larger than those represented by themagnetization curves of the spinel thin film to which a magnetic fieldwas applied in the in-plane direction, the spinel thin film wasrecognized as a perpendicular magnetic film. As to the magneticcharacteristics of the perpendicular magnetic film, the saturationmagnetization was 280 emu/cc (3500 G), the coercive force was 108 kOe,and the squareness was 0.64. The spacing of the plane (400) was 2.078 Å.

Comparative Example 1

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 200° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 56 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar ratio of Ni to Co is 0.24) to a thickness of 7 Å as a secondlayer by sputtering the Co--Ni target at a deposition rate of 42 Å/min.The first layer and the second layer constituted one unit having athickness of 63 Å. The molar ratio of Co to Fe in one unit was 0.15.These operations were alternately repeated 68 times to obtain amultilayered film composed of 34 Fe₃ O₄ layers each having a thicknessof 56 Å, and 34 Co- and Ni-containing oxide layers each having athickness of 7 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate.

The obtained multilayered film was annealed in the air at a temperatureof 400° C. for 1 hour so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

Since the residual magnetization and the coercive force of thethus-obtained spinel thin film represented by the magnetization curvesof the spinel thin film to which a magnetic field was applied in theperpendicular direction were larger than those represented by themagnetization curves of the spinel thin film to which a magnetic fieldwas applied in the in-plane direction, the spinel thin film wasrecognized as a perpendicular magnetic film. As to the magneticcharacteristics of the perpendicular magnetic film, the saturationmagnetization was 290 emu/cc (3600 G), the coercive force was 4.4 kOe,and the squareness was 0.77. The spacing of the plane (400) was 2.077 Å.

Comparative Example 2

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co--Ni targetand the substrate temperature was held at 280° C. Reactive sputteringwas first carried out by using the Fe target in an atmosphere of argonand oxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 56 Å as afirst layer.

The shutter was next rotated to form a Co- and Ni-containing oxide layer(the molar ratio of Ni to Co is 0.57) to a thickness of 7 Å as a secondlayer by sputtering the Co--Ni target at a deposition rate of 42 Å/min.The first layer and the second layer constituted one unit having athickness of 63 Å. The molar ratio of Co to Fe in one unit was 0.15.These operations were alternately repeated 68 times to obtain amultilayered film composed of 34 Fe₃ O₄ layers each having a thicknessof 56 Å, and 34 Co- and Ni-containing oxide layers each having athickness of 7 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co--Ni side. In the thus-obtained multilayered film,the plane (400) was predominantly oriented in parallel with thesubstrate.

The obtained multilayered film was annealed in the air at a temperatureof 400° C. for 1 hour so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo and Ni, thereby producing a spinel thin film containing Fe as themain ingredient and further containing Co and Ni. As a result of theX-ray diffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

Since the residual magnetization and the coercive force of thethus-obtained spinel thin film represented by the magnetization curvesof the spinel thin film to which a magnetic field was applied in theperpendicular direction were larger than those represented by themagnetization curves of the spinel thin film to which a magnetic fieldwas applied in the in-plane direction, the spinel thin film wasrecognized as a perpendicular magnetic film. As to the magneticcharacteristics of the perpendicular magnetic film, the saturationmagnetization was 270 emu/cc (3400 G), the coercive force was 3.1 kOe,and the squareness was 0.70. The spacing of the plane (400) was 2.077 Å.

Comparative Example 3

A multilayered film was produced in the same way as in Example 1 exceptthat the thickness of the spinel Fe₃ O₄ film was 345 Å, the thickness ofthe Co- and Ni-containing oxide layer (the molar ratio of Co to Fe was0.02, and the molar ratio of Ni to Co was 2.0) was 15 Å, the thicknessof one unit was 360 Å, and the multilayered film was composed of 5 Fe₃O₄ layers each having a thickness of 345 Å, and 5 Co- and Ni-containingoxide layers each having a thickness of 15 Å.

The X-ray diffraction spectrum of the multilayered film obtained isshown in FIG. 1(a) . As shown in FIG. 1(a), the planes (311) and (222)were proved to predominantly orient in parallel with the substrate.

By using the multi layered film obtained, a spinel oxide film wasproduced in the same way as in Example 1. As a result of the X-raydiffraction of the spinel oxide film obtained, the planes (311) and(222) were proved to predominantly orient in parallel with thesubstrate. From the observation of the magnetization curve of the spineloxide film, it was found that the residual magnetization and thecoercive force of the film to which a magnetic field was applied in thein-plane direction were larger than those of the film to which amagnetic field was applied in the perpendicular direction. Thus, it wasproved that the film was not a perpendicular magnetic film.

Comparative Example 4

A multilayered film was produced in the same way as in Example 1 exceptthat the thickness of the spinel Fe₃ O₄ film was 36 Å, the thickness ofthe Co- and Ni-containing oxide layer (the molar ratio of Co to Fe was0.69, and the molar ratio of Ni to Co was 1.5) was 17 Å, the thicknessof one unit was 53 Å, and the multilayered film was composed of 60 Fe₃O₄ layers each having a thickness of 36 Å, and 60 Co- and Ni-containingoxide layers each having a thickness of 17 Å.

The X-ray diffraction spectrum of the multilayered film obtained isshown in FIG. 1(b). As shown in FIG. 1(b), the plane (400) was proved topredominantly orient in parallel with the substrate.

By using the multilayered film obtained, a spinel oxide film wasproduced in the same way as in Example 1. As a result of the X-raydiffraction of the spinel oxide film obtained, the plane (400) wasproved to predominantly orient in parallel with the substrate. From theobservation of the magnetization curve of the spinel oxide film, it wasfound that the residual magnetization and the coercive force of the filmto which a magnetic field was applied in the in-plane direction werelarger than those of the film to which a magnetic field was applied inthe perpendicular direction. Thus, it was proved that the film was not aperpendicular magnetic film.

Reference Example 1

In a high-frequency high-rate sputtering device SH-250H-T06,manufactured by Nippon Shinku Kabushiki Kaisha, a glass substrate wasplaced with a distance of 80 mm from an Fe target and a Co target andthe substrate temperature was held at 280° C. Reactive sputtering wasfirst carried out by using the Fe target in an atmosphere of argon andoxygen under a partial oxygen pressure of 0.11 mTorr and the totalpressure of 5 mTorr at a deposition rate of 40 Å/min, thereby forming aspinel Fe₃ O₄ layer on the glass substrate to a thickness of 40 Å as afirst layer.

The shutter was next rotated to form a CoO layer to a thickness of 7 Åas a second layer by sputtering the Co target at a deposition rate of 42Å/min. The first layer and the second layer constituted one unit havinga thickness of 47 Å. The molar ratio of Co to Fe in one unit was 0.26.These operations were alternately repeated 100 times to obtain amultilayered film composed of 50 Fe₃ O₄ layers each having a thicknessof 40 Å, and 50 CoO layers each having a thickness of 7 Å.

The making power at the time of film formation was 300 W on the Fe sideand 300 W on the Co side. In the thus-obtained multilayered film, theplane (400) was predominantly oriented in parallel with the substrate.

The obtained multilayered film was annealed in the air at a temperatureof 450° C. for 1 hour so as to oxidize Fe₃ O₄ into γ-Fe₂ O₃ and diffuseCo, thereby producing a spinel thin film containing Fe as the mainingredient and further containing Co. As a result of the X-raydiffraction of the film obtained, the plane (400) was proved topredominantly orient in parallel with the substrate.

Since the residual magnetization and the coercive force of thethus-obtained spinel thin film represented by the magnetization curvesof the spinel thin film to which a magnetic field was applied in theperpendicular direction were larger than those represented by themagnetization curves of the spinel thin film to which a magnetic fieldwas applied in the in-plane direction, the spinel thin film wasrecognized as a perpendicular magnetic film. As to the magneticcharacteristics of the perpendicular magnetic film, the saturationmagnetization was 340 emu/cc (4250 G), the coercive force was 5.4 kOe,and the squareness was 0.75. The spacing of the plane (400) was 2.082 Å.

What is claimed is:
 1. A perpendicular magnetic film comprising a spinelthin film having a spinel crystal structure, consisting essentially ofFe, Co, Ni and O, and having a coercive force of less than 3000 Oe, asaturation magnetization of not less than 200 emμ/cc and a squareness ofnot less than 0.20,the thin film being formed on a substrate, the plane(400) of the thin film being oriented substantially parallel to saidsubstrate so that the spacing of the plane (400) is not more than 2.082Å, the molar ratio of Co to Fe in the thin film being 0.005 to 0.32 andthe molar ratio of Ni to Co in the thin film being not less than 0.6. 2.A perpendicular magnetic film according to claim 1, wherein said filmhas a thickness of 500 to 5000 Å.
 3. A perpendicular magnetic filmaccording to claim 1, wherein said coercive force is 1200 to 2500 Oe. 4.A perpendicular magnetic film according to claim 1, which is produced byannealing at a temperature of 280° to 450° C. a Co- and Ni-containingmultilayered film comprising a multiplicity of multilayered units formedon a substrate, each unit composed of:(1) a magnetite FeOx·Fe₂ O₃(0<x≦1) layer or a magnetite FeO_(x) ·Fe₂ O₃ (0<x≦1) layer which alsocontains Co, Ni or a mixture of Co and Ni diffused into the magnetite,and (2) an oxide layer comprising Co, Ni or a mixture of Co and Ni,provided that the magnetite layer (1) and the oxide layer (2) aremultilayered so as to contain both Co and Ni in each of the units(1)+(2), the plane (400) of each magnetite layer (1) in the units beingoriented substantially parallel to said substrate, each unit having athickness of not more than 300 Å, the molar ratio of Co to Fe in themultilayered film being 0.005 to 0.32, and the molar ratio of Ni to Coin the multilayered film being not less than 0.6.